U.S. patent application number 14/350251 was filed with the patent office on 2015-01-01 for reshaping thin glass sheets.
The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Antoine Gaston Denis Bisson, Curtis Richard Cowles, Laurent Joubaud, David John McEnroe, Aniello Mario Palumbo.
Application Number | 20150000341 14/350251 |
Document ID | / |
Family ID | 48082724 |
Filed Date | 2015-01-01 |
United States Patent
Application |
20150000341 |
Kind Code |
A1 |
Bisson; Antoine Gaston Denis ;
et al. |
January 1, 2015 |
RESHAPING THIN GLASS SHEETS
Abstract
An apparatus and methods for bending sheet glass are disclosed.
The present invention improves on the state-of-the-art by providing
apparatus and methods that prevent unwanted distortion of the glass
sheet. The apparatus and methods utilize localized heating at the
bend to allow for overall glass sheet temperatures to be reduced,
along with optional mechanical devices for improved bend
quality.
Inventors: |
Bisson; Antoine Gaston Denis;
(Corning, NY) ; Cowles; Curtis Richard; (Corning,
NY) ; Joubaud; Laurent; (Paris, FR) ; McEnroe;
David John; (Corning, NY) ; Palumbo; Aniello
Mario; (Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
CORNING |
NY |
US |
|
|
Family ID: |
48082724 |
Appl. No.: |
14/350251 |
Filed: |
October 5, 2012 |
PCT Filed: |
October 5, 2012 |
PCT NO: |
PCT/US12/58950 |
371 Date: |
April 7, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61545329 |
Oct 10, 2011 |
|
|
|
Current U.S.
Class: |
65/106 ;
65/273 |
Current CPC
Class: |
C03B 23/0235 20130101;
C03B 23/0258 20130101; C03B 23/0256 20130101; C03B 23/0357
20130101 |
Class at
Publication: |
65/106 ;
65/273 |
International
Class: |
C03B 23/023 20060101
C03B023/023; C03B 23/025 20060101 C03B023/025 |
Claims
1. An apparatus for bending a glass sheet comprising: a. a support
element; b. an overall heating device; c. a localized heating
device; and d. a bending assistance device which contacts said
glass sheet: i. outside of the bending area; and ii. on the side of
the bending area opposite said support element.
2. The apparatus of claim 1, further comprising a constraint device
which contacts said glass sheet outside of the bending area.
3. The apparatus of claim 1, wherein said localized heating device
comprises a device that heats said glass sheet by a method
comprising conduction or radiation.
4. The apparatus of claim 3, wherein said localized heating device
comprises a device that heats said glass sheet by conduction.
5. The apparatus of claim 4, wherein said conduction element
comprises a metal, metal oxide, carbon compound, intermetallic
compound, ceramic, or glass ceramic.
6. The apparatus of claim 5, wherein said conduction element
comprises platinum, nichrome, kanthal, cupronickel, doped or
undoped molybdenum disilicide, metal ceramics, calrod, a positive
thermal coefficient ceramic, barium titanate, lead titanate,
molybdenum, or silicon carbide.
7. The apparatus of claim 3, wherein said localized heating device
comprises a device that heats said glass sheet by a method
comprising radiation.
8. The apparatus of claim 3, wherein said localized heating device
comprises an infrared heater.
9. The apparatus of claim 1, wherein said bending assistance device
comprises a mechanically moveable device that contacts said glass
sheet throughout the entire bending process.
10. The apparatus of claim 1, wherein said bending assistance
device comprises a ceramic, glass ceramic, metal, or metal
oxide.
11. The apparatus of claim 2, wherein said constraint device
comprises a mechanically moveable device that contacts said glass
sheet only while said glass sheet is being bent.
12. The apparatus of claim 2, wherein said constraint device
comprises a fixed device that contacts said glass sheet at a point
comprising an unwanted deformation only when said glass sheet
unwantedly deforms outside the bend region.
13. The apparatus of claim 2, wherein said constraint device
comprises a fixed device that contacts said glass sheet at a point
comprising an unwanted deformation only when said glass sheet
unwantedly deforms outside the bend region.
14. The apparatus of claim 2, wherein said constraint device
comprises a ceramic, glass ceramic, metal, or metal oxide.
15. The apparatus of claim 2, wherein said constraint device
further comprises a heat sink.
16. A method of bending a glass sheet comprising: a. providing the
apparatus of claim 1; b. providing an initial glass sheet; c.
positioning the initial glass sheet in the apparatus of claim 1; d.
applying a bending assistance device to said initial glass sheet;
e. overall heating said initial glass sheet; f. locally heating a
section of said initial glass sheet; and g. bending at least one
part of said initial glass sheet.
17. The method of claim 16, further comprising the step of applying
a constraint device to said initial glass sheet.
18. The method of claim 16, wherein said applying a bending
assistance device to said initial glass sheet comprises applying
said bending assistance device throughout the entire bending
process.
19. The method of claim 17, wherein said applying a constraint
device to said initial glass sheet comprises applying said
constraint device only while the glass sheet is being bent.
20. The method of claim 17, wherein said applying a constraint
device to said initial glass sheet comprises application of a fixed
device that contacts said glass sheet at a point comprising an
unwanted deformation only when said glass sheet unwantedly deforms
outside the bend region.
21. The method of claim 16, wherein said initial glass sheet
comprises an ion exchangeable, soda-lime silicate, alkali
borosilicate, or alumina borosilicate glass sheet.
22. The method of claim 16, wherein said overall heating comprises
heating said initial glass sheet to a temperature wherein the
viscosity of the glass sheet is from about 10.sup.10 to about
10.sup.21 Poise.
23. The method of claim 16, wherein said locally heating comprises
heating said section of said initial glass sheet to a temperature
wherein the viscosity of the glass is from about 10.sup.7 to about
10.sup.14 Poise.
Description
RESHAPING THIN GLASS SHEETS
[0001] This application claims the benefit of priority under 35 USC
.sctn.119 of U.S. Provisional Application Ser. No. 61/545,329 filed
Oct. 10, 2011 the content of which is relied upon and incorporated
herein by reference in its entirety.
FIELD
[0002] The present disclosure relates generally to apparatus and
methods for forming tight bends and shapes in thin glass sheets.
The apparatus and methods provide the ability to reshape thin glass
sheets into complex geometries with minimal distortion while
retaining the surface quality of the glass. Additional advantages
include use with large sheet glass sizes, lower preheating
temperatures, and shorter cycle times, all of which result in cost
savings.
BACKGROUND
[0003] The emergence of chemically strengthen glass, especially
glass that can be manufactured in large thin sheet sizes by fusion
forming, has opened up market segments in a variety of consumer
areas. These new markets include the use of thin sheet glass in
electronic devices for displays, appliances, and automotive
components. Examples of potential applications include liquid
crystal displays (LCDs), electrophoretic displays (EPD), organic
light emitting diode displays (OLEDs), plasma display panels
(PDPs), and the like. In particular, the expanding use of ion
exchangeable thin sheet glass in these markets has prompted the
desire for shaped three-dimensional glass sheets, with an emphasis
on combinations of flat portions with highly curved, localized
shapes.
[0004] Currently, glass sheets are commonly fabricated by a flowing
molten glass to a forming body whereby a glass ribbon may be formed
by a variety of ribbon forming process techniques, for example,
slot draw, float, down-draw, fusion down-draw, or up-draw. The
glass ribbon may then be subsequently divided to provide sheet
glass suitable for further processing into a desired application.
Subsequent fabrication techniques that allow for modification of
the shape of the glass sheet are desirable to extend the number of
applications wherein flat glass could be used. A good example is
the case of automotive windshields, where current designs are far
from simple flat shapes.
[0005] However, there are significant challenges to modifying the
shape of thin flat glass sheets. For display applications, optical
clarity of the glass sheet is extremely important and maintaining
the "pristine" nature of the fusion formed surface is critical.
Standard molding techniques used for bending and reshaping sheet
glass tend to imprint any irregularities the mold tooling may have
onto the glass surface, therefore a shaping technique which limits
the amount of contact the tooling has with the display area of the
glass is preferred. Additionally, the demand for tighter controlled
deformations (e.g., bends) and thinner glass sheets, typically 1 mm
thickness or less, means that the traditional processes for bending
glass sheets are not suitable as they are unable to cleanly create
the necessary structures.
[0006] Thus, there is a need for processes which allow: retention
of a high level of flatness in the desired areas, usually the
largest area of the finished product; retention of the pristine
aspect of the glass sheet; desired amount of deformation in the
areas of interest; and a high level of dimensional control.
Embodiments address these needs by allowing for bending and shaping
sheet glass using targeted heating optionally with clamping and/or
mechanical means to avoid unwanted distortions in the glass sheet
while avoiding or minimizing contact with the glass. Such processes
can be suitable for reforming glass sheets in a wide range of
applications incorporating glass sheets such as appliances (e.g.
display applications), automotive, portable electronic devices, or
other devices incorporating a reformed glass sheet.
SUMMARY
[0007] An aspect of the disclosure is to provide apparatus and
methods for reforming sheet glass. More particularly, an object of
the present disclosure is to provide apparatus and methods for
bending sheet glass with little or no unwanted distortion to the
glass sheet at points outside of the bend.
[0008] A first embodiment is an apparatus for bending a glass sheet
a support element that supports the body of said glass sheet, an
overall heating device, a localized heating device that heats a
portion of said glass sheet to a temperature sufficiently high
enough to allow said portion of said glass sheet to bend, and a
bending assistance device which contacts said glass sheet outside
of the bending area and on the side of the bending area opposite
said support element. In some embodiments, said localized heating
device comprises a device that heats said glass sheet by a method
comprising conduction, convection, or radiation. In some
embodiments, said localized heating device comprises a conduction
element. In some embodiments, said conduction element comprises a
metal, metal oxide, carbon compound, intermetallic compound,
ceramic, or glass ceramic. In some embodiments, said conduction
element comprises platinum, nichrome, kanthal, cupronickel, doped
or undoped molybdenum disilicide, metal ceramics, calrod, a
positive thermal coefficient ceramic, barium titanate, lead
titanate, molybdenum, or silicon carbide. In some embodiments, said
bending assistance device comprises a mechanically moveable device
that contacts said glass sheet throughout the entire bending
process. In some embodiments, said bending assistance device
comprises a ceramic, glass ceramic, metal, or metal oxide.
[0009] Another embodiment is an apparatus for bending a glass sheet
comprising a support element that supports the body of said glass
sheet, an overall heating device, a localized heating device that
heats a portion of said glass sheet to a temperature sufficiently
high enough to allow said portion of said glass sheet to bend, and
a constraint device which contacts said glass sheet outside of the
bending area. In some embodiments, said localized heating device
comprises a device that heats said glass sheet by a method
comprising conduction, convection, or radiation. In some
embodiments, said localized heating device comprises a device that
heats said glass sheet by a method comprising radiation. In some
embodiments, said localized heating device comprises an infrared
heater. In some embodiments, said constraint device comprises a
mechanically moveable device that contacts said glass sheet only
while said glass sheet is being bent. In some embodiments, said
constraint device comprises a fixed device that contacts said glass
sheet at a point comprising an unwanted deformation only when said
glass sheet unwantedly deforms outside the bend region. In some
embodiments, said constraint device comprises a ceramic, glass
ceramic, metal, or metal oxide. In some embodiments, said overall
heating device heats said glass sheet to a temperature below the
glass transition temperature of said glass sheet. In some
embodiments, said constraint device further comprises a vacuum or
air pressure device.
[0010] Another embodiment is an apparatus for bending a glass sheet
comprising a support element that supports the body of said glass
sheet, an overall heating device, a localized heating device that
heats a portion of said glass sheet to a temperature sufficiently
high enough to allow said portion of said glass sheet to bend, a
constraint device which contacts said glass sheet outside of the
bending area, and a bending assistance device which contacts said
glass sheet outside of the bending area and on the side of the
bending area opposite said support element. In some embodiments,
said localized heating device comprises a device that heats said
glass sheet by a method comprising conduction, convection, or
radiation. In some embodiments, said localized heating device
comprises an infrared heater. In some embodiments, said localized
heating device comprises a conduction element. In some embodiments,
said conduction element comprises a metal, metal oxide, carbon
compound, intermetallic compound, ceramic, or glass ceramic. In
some embodiments, said conduction element comprises platinum,
nichrome, kanthal, cupronickel, doped or undoped molybdenum
disilicide, metal ceramics, calrod, a positive thermal coefficient
ceramic, barium titanate, lead titanate, molybdenum, or silicon
carbide. In some embodiments, said bending assistance device
comprises a mechanically moveable device that contacts said glass
sheet throughout the entire bending process. In some embodiments,
said bending assistance device comprises a ceramic, glass ceramic,
metal, or metal oxide. In some embodiments, said constraint device
comprises a mechanically moveable device that contacts said glass
sheet only while said glass sheet is being bent. In some
embodiments, said constraint device comprises a fixed device that
contacts said glass sheet at a point comprising an unwanted
deformation only when said glass sheet unwantedly deforms outside
the bend region. In some embodiments, said constraint device
comprises a ceramic, glass ceramic, metal, or metal oxide. In some
embodiments, said overall heating device heats said glass sheet to
a temperature below the glass transition temperature of said glass
sheet. In some embodiments, said constraint device further
comprises a vacuum or air pressure device.
[0011] Another embodiment is a method of bending a glass sheet
comprising providing an embodiment of the apparatus, providing an
initial glass sheet, positioning said initial glass sheet in said
apparatus, applying a bending assistance device to said initial
glass sheet, overall heating said initial glass sheet, locally
heating a section of said initial glass sheet, and bending at least
one part of said initial glass sheet. In some embodiments, said
applying a bending assistance device to said initial glass sheet
comprises applying said bending assistance device throughout the
entire bending process. In some embodiments, said initial glass
sheet comprises an ion exchangeable, soda-lime silicate, EAGLE
XG.RTM., 0211-type, or alkali borosilicate glass sheet. In some
embodiments, said overall heating comprises heating said initial
glass sheet to a temperature below the glass transition temperature
of said glass sheet. In some embodiments, said locally heating
comprises heating said section of said initial glass sheet to about
the glass transition temperature of said initial glass sheet. In
some embodiments, the method further comprises annealing said glass
sheet.
[0012] Another embodiment is a method of bending a glass sheet
comprising providing an embodiment of the apparatus, providing an
initial glass sheet, positioning said initial glass sheet in said
apparatus, overall heating said initial glass sheet, locally
heating a section of said initial glass sheet, applying a
constraint device to said initial glass sheet, and bending at least
one part of said initial glass sheet. In some embodiments, said
applying a constraint device to said initial glass sheet comprises
applying said constraint device only while the glass is being bent.
In some embodiments, said initial glass sheet comprises an ion
exchangeable, soda-lime silicate, EAGLE XG.RTM., 0211-type, or
alkali borosilicate glass sheet. In some embodiments, said overall
heating comprises heating said initial glass sheet to a temperature
below the glass transition temperature of said glass sheet. In some
embodiments, said locally heating comprises heating said section of
said initial glass sheet to about the glass transition temperature
of said initial glass sheet. In some embodiments, the method
further comprises annealing said glass sheet.
[0013] Another embodiment is a method of bending a glass sheet
comprising providing an embodiment of the apparatus, providing an
initial glass sheet, positioning said initial glass sheet in said
apparatus, applying a bending assistance device to said initial
glass sheet, overall heating said initial glass sheet, locally
heating a section of said initial glass sheet, applying a
constraint device to said initial glass sheet, and bending at least
one part of said initial glass sheet. In some embodiments, said
applying a bending assistance device to said initial glass sheet
comprises applying said bending assistance device throughout the
entire bending process. In some embodiments, said applying a
constraint device to said initial glass sheet comprises applying
said constraint device only while the glass is being bent. In some
embodiments, said initial glass sheet comprises an ion
exchangeable, soda-lime silicate, EAGLE XG.RTM., 0211-type, or
alkali borosilicate glass sheet. In some embodiments, said overall
heating comprises heating said initial glass sheet to a temperature
below the glass transition temperature of said glass sheet. In some
embodiments, said locally heating comprises heating said section of
said initial glass sheet to about the glass transition temperature
of said initial glass sheet. In some embodiments, the method
further comprises annealing said glass sheet.
[0014] In some embodiments, the process further comprises a
post-bending treatment process. In some embodiments the
post-bending treatment process comprises a cooling step wherein the
bent glass sheet is allowed to cool to the overall heated
temperature in the overall heating device prior to removal. In some
embodiments, the process further comprises retaining the bent glass
sheet in the overall heating device or placing the bent glass sheet
in a separate heating device, to allow for post-bending treatment.
In some embodiments, post-bending treatment comprises
annealing.
[0015] In another embodiment, the process comprises overall heating
the glass sheet in a first overall heating device, moving the glass
sheet to an embodiment of the apparatus, which may, optionally, be
in a second overall heating device, bending the initial glass
sheet, and then optionally, moving the bent glass sheet to either
the first overall heating device or to a third overall heating
device for post-bending treatment.
[0016] Advantages of embodiments include: the ability to reshape
thin glass sheets with minimal distortion and good geometrical
control; a reshaping process that can maintain the surface quality
of a fusion formed glass sheet; flexibility in the forming process
to reshape complex geometries along with variable curvatures and
angles; sheet size (final product size) not limited by process, but
only dependent on furnace and/or device size; mold less process, no
glass surface irregularities from mold contact; and edge bending of
glass sheet with <2 mm radius of curvature possible.
[0017] It is to be understood that both the foregoing summary and
the following detailed description are merely exemplary, and are
intended to provide an overview or framework to understanding the
nature and character of the claims. The accompanying drawings are
included to provide a further understanding, and are incorporated
in and constitute a part of this specification. The drawings
illustrate one or more embodiment(s), and together with the
description serve to explain principles and operation of the
various embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1. Pictoral representation of a thin glass sheet
showing a 90.degree. bend and identifying the bending area as the
region between the section lines highlighted by the circle.
[0019] FIG. 2. Embodiment of the direct-fired platinum-tube process
set up: this drawing shows an embodiment wherein a glass sheet is
placed on a refractory frame with two platinum tubes positioned
parallel to each other at each end of the glass sheet and an
embodiment of the bending assistance device placed on top of the
ends of the glass sheet.
[0020] FIG. 3. A schematic of an embodiment of the bending device
before bending: the drawing represents the positioning of the
ceramic tubes and support brackets prior to the bending of the
sheet.
[0021] FIG. 4. A schematic of an embodiment of the bending device
after bending: the drawing represents the positioning of the
ceramic tubes and support brackets after bending the glass
sheet.
[0022] FIG. 5. An illustration (FIG. 5A) of the process layout for
a case where two linear bends are to be made on a flat glass part.
Reference number 4 denotes the glass sheet, reference number 2
denotes an embodiment of the support element, reference number 3
describes the bending regions, reference number 6 is the region
that is locally heated to deform, 7 is the region of the glass from
the edge to the bending region, and reference number 8 refers to
the thickness of the glass sheet. FIG. 5B is a graph of the surface
map of the sample, showing a bump in the vicinity of the bent
area.
[0023] FIG. 6. An illustration (FIG. 6A) of the process described
in FIG. 5A, with the addition of an embodiment of the constraint
device, reference number 1 onto the glass, in the vicinity of the
area to bend. Reference number 3 describes the bending regions, 6
is the region that is locally heated, reference number 7 is the
region of the glass from the edge to the bending region, and
reference number 8 refers to the thickness of the glass sheet. The
load may be actuated to contact the glass only when required. FIG.
6B is a graph of the surface map of the sample one showing the
stability of the sample when the constraint device is applied.
[0024] FIG. 7. A schematic representation of the process window
regarding the stability of the flat part of the glass sheet. A
relation between preheating temperature and local heating rate
defines the stable and unstable domains. High local heating rates
are desired to decrease cycle time and radius of curvature, while
lower preheating temperatures are desired to maintain optical
surface quality and shape. The curve position is correlated with
bend length, where longer bends shift the curve down.
[0025] FIG. 8. FIGS. 8A-D show various embodiments of the
constraint device and their location relative to the support
element and glass sheet. All figures are drawn in the X-Z plane.
FIG. 8A shows the constraint device, 1, applying force on top of
the support element, 2, with the bending area noted as 3. FIG. 8B
shows the constraint device, 1, applying force outside of the
support element, 2, via vacuum pressure, with the bending area
noted as 3. FIG. 8C shows the constraint device, 1, applying force
on top of the support element, 2, via vacuum pressure, with the
bending area noted as 3. FIG. 8D shows the constraint device, 1,
applying force from below and either from within the support
element or outside of the support element, 2, via vacuum pressure,
with the bending area noted as 3.
[0026] FIG. 9. FIGS. 9A-B show embodiments of the constraint device
wherein the constraint device only contacts the glass sheet if the
glass sheet unwantedly deforms in a region outside the bending
area. FIG. 9A is a schematic of the device in the X-Z plane wherein
the constraint device, 1, is positioned within a few hundred
micrometers of the glass sheet, but is not touching it. The glass
is supported on the support element, 2, and bent via heating of the
bending region, 3. FIG. 9B shows the Y-Z plane of the device in
FIG. 9A, wherein 1 again represents the rigid constraint device
that is spaced slightly away from the glass sheet, 4, and only
contacts the glass if the glass unwantedly deforms. Additionally,
the support element is noted by 2.
[0027] FIG. 10. Picture showing glass sheets having various bend
radii of 2, 3, and 5 mm from the end edge perspective.
[0028] FIG. 11. A picture of a 5 mm bend radius along with
measurement points.
[0029] FIG. 12. A picture of 3 mm bend radius along with
measurement points.
[0030] FIG. 13. A picture of a 2 mm bend radius along with
measurement points.
DETAILED DESCRIPTION
[0031] The present disclosure can be understood more readily by
reference to the following detailed description, drawings,
examples, and claims, and their previous and following description.
However, before the present compositions, articles, devices, and
methods are disclosed and described, it is to be understood that
this disclosure is not limited to the specific compositions,
articles, devices, and methods disclosed unless otherwise
specified, as such can, of course, vary. It is also to be
understood that the terminology used herein is for the purpose of
describing particular aspects only and is not intended to be
limiting.
[0032] The following description is provided as an enabling
teaching. To this end, those skilled in the relevant art will
recognize and appreciate that many changes can be made to the
various aspects described herein, while still obtaining the
beneficial results. It will also be apparent that some of the
desired benefits can be obtained by selecting some of the disclosed
without utilizing other features. Accordingly, those who work in
the art will recognize that many modifications and adaptations are
possible and can even be desirable in certain circumstances and are
a part of the disclosure. Thus, the following description is
provided as illustrative and not in limitation thereof.
[0033] Disclosed are materials, compounds, compositions, and
components that can be used for, can be used in conjunction with,
can be used in preparation for, or are embodiments of the disclosed
method and compositions. These and other materials are disclosed
herein, and it is understood that when combinations, subsets,
interactions, groups, etc. of these materials are disclosed that
while specific reference of each various individual and collective
combinations and permutation of these compounds may not be
explicitly disclosed, each is specifically contemplated and
described herein. Thus, if a class of substituents A, B, and C are
disclosed as well as a class of substituents D, E, and F, and an
example of a combination embodiment, A-D is disclosed, then each is
individually and collectively contemplated. Thus, in this example,
each of the combinations A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F
are specifically contemplated and should be considered disclosed
from disclosure of A, B, and C; D, E, and F; and the example
combination A-D. Likewise, any subset or combination of these is
also specifically contemplated and disclosed. Thus, for example,
the sub-group of A-E, B-F, and C-E are specifically contemplated
and should be considered disclosed from disclosure of A, B, and C;
D, E, and F; and the example combination A-D. This concept applies
to all aspects of this disclosure including, but not limited to any
components of the compositions and steps in methods of making and
using the disclosed compositions. Thus, if there are a variety of
additional steps that can be performed it is understood that each
of these additional steps can be performed with any specific
embodiment or combination of embodiments of the disclosed methods,
and that each such combination is specifically contemplated and
should be considered disclosed.
[0034] In this specification and in the claims which follow,
reference will be made to a number of terms which shall be defined
to have the following meanings:
[0035] "Include," "includes," or like terms means encompassing but
not limited to, that is, inclusive and not exclusive.
[0036] The term "about" references all terms in the range unless
otherwise stated. For example, about 1, 2, or 3 is equivalent to
about 1, about 2, or about 3, and further comprises from about 1-3,
from about 1-2, and from about 2-3. Specific and preferred values
disclosed for compositions, components, ingredients, additives, and
like aspects, and ranges thereof, are for illustration only; they
do not exclude other defined values or other values within defined
ranges. The compositions and methods of the disclosure include
those having any value or any combination of the values, specific
values, more specific values, and preferred values described
herein.
[0037] The indefinite article "a" or "an" and its corresponding
definite article "the" as used herein means at least one, or one or
more, unless specified otherwise.
[0038] The term "support element" refers to an object used to
support the glass sheet within the apparatus. The support element
may comprise any shape that allows for placement of the glass sheet
in the apparatus, supports the glass sheet, and allows for the
glass sheet to be bent. The support element typically supports the
major portion, or "body," of the glass sheet. The support element
may contact the glass sheet on either one or both faces, or may
change contact points as the glass is processed. The support
element may be designed to allow for multiple bends to be done
without moving the glass sheet, or for multiple bends to be done
simultaneously. Further, the support element may allow for complex
shapes or bends to be made to the glass sheet, for example by
comprising a support that is flexible, or can change shape.
Examples of support elements include, but are not limited to,
solid- or honeycomb-type plates or surfaces, external support
frames, support columns, rollers or conveyers, or elements that
produce air pressure or vacuum pressure. In the case of elements
that produce air pressure or vacuum pressure, it may be the case
that such elements allow the glass sheet to avoid physical contact
with a solid support.
[0039] The term "overall heating device" refers to a heating device
that may be used to heat the entire glass sheet simultaneously, and
may optionally also heat the support element, constraint device
and/or the bending assistance device. The overall heating device
may heat the glass sheet by any known heating process and may
operate by, but is not limited to, resistance heating, combustion
heating, induction heating, or electromagnetic heating. Heat
transfer from the overall heating device to the glass sheet may
occur via convection, conduction, or radiation. Examples of
embodiments of overall heating devices include, but are not limited
to kilns, such as a lehr or tunnel kiln, or static furnaces that
may be bottom loaded or of a top hat type. Additionally, the
overall heating device may comprise multiple heating devices, which
optionally, may be used in individually in different process
steps.
[0040] The term "localized heating device" refers to a heating
device which only heats a portion of the glass sheet. The localized
heating device may heat the glass sheet by any known heating
process and may operate by, but is not limited to, resistance
heating, combustion heating, induction heating, or electromagnetic
heating, such as infrared, laser or microwave heating. Heat
transfer from the overall heating device to the glass sheet may
occur via convection, conduction, or radiation. Examples of
embodiments of localized heating devices include, but are not
limited to infrared heaters, lasers, burners, or shaped metal
contacts, such as platinum, silicon carbide, or molybdenum
disilicide rods, which conduct heat to the glass sheet. In some
embodiments, the localized heating device may be used
contemporaneously with the overall heating device, but it may also
be used subsequent to the overall heating device.
[0041] The term "bending assistance device" refers to an element in
contact with, or applying force to, the non-bending part of the
glass substrate at a point outside the localized heating area and
that is capable of providing additional control to the bending
process. The bending assistance device may comprise any shape or
structure that allows for it to contact or apply force to the glass
sheet and assist in bending the glass and/or allows the device to
perform the function of improving the bend properties and/or bend
characteristics, allows for bending of the glass sheet at lower
temperatures, and/or reduces the time needed for bending the glass
sheet. Examples of embodiments of bending assistance devices
include, but are not limited to, rollers or wheels on rotating
brackets attached to the support element that contact the glass
sheet and allow for the contact point between the bending
assistance device and the glass sheet to move as the sheet
bends.
[0042] The term "constraint device" refers to an element in contact
with, or applying force to, the non-bending part of the glass
substrate at a point on the same side of the bend as the support
element that is capable of limiting unwanted distortions or
deformations to the glass sheet as a result of the bending process.
The constraint device may comprise any shape or structure that
allows for it to contact or apply force to the glass sheet and
prevent unwanted deformation in the glass sheet. Examples of
embodiments of the constraint device, include, but are not limited
to, solid- or honeycomb-type plates or surfaces, external support
frames, columns or rollers, or elements that produce air pressure
or vacuum pressure. In the case of elements that produce air
pressure or vacuum pressure, it may be the case that such elements
allow the glass sheet to avoid physical contact with a constraint
device.
[0043] When reshaping many glasses, such as current ion
exchangeable glasses that are fusion formable, the entire sheet has
to be heated to avoid cracking. This requires heating the entire
sheet, for example in a furnace, and then reshaping it before it
can cool down. However, to maintain flatness of the portion of the
sheet area where reshaping is not desired, i.e., outside the
bending area (see FIG. 1), a minimum temperature for the overall
heating of the sheet may be preferred. Lower overall temperatures
improve the surface quality of the flat portion of the glass sheet,
as the sheet is less likely to show marks or damage where it has
contacted any solid elements (e.g., the support element, bending
assistance device and/or the constraint device). Further, elevated
overall temperature can create distortions in the flat regions of
the sheet or create uneven bending geometries.
[0044] One aspect is to allow for lowering of the overall
temperature of the glass sheet during the bending process. As
compared to other glass sheet bending devices and process,
embodiments may be used with thinner glasses and/or glasses having
higher thermal expansion glass compositions (such as ion
exchangeable glasses which have a high CTE) with fewer occurrences
of instabilities.
[0045] Some embodiments enable bending and shaping of flat sheets
of glass using overall heating below the glass transition state
along with localized heating in the bend region to form a select
bend region. In some embodiments, the bending and shaping of flat
sheets of glass comprises using overall heating below the softening
point along with localized heating in the bend region to form a
select bend region.
[0046] In some embodiments, the glass sheet comprises multiple
layers of glass, which may be laminated. In some embodiments, the
layers of glass comprise different glass compositions.
[0047] Other embodiments enable bending and shaping of flat sheets
of glass using overall heating along with localized heating in the
bend region to form a select bend region. Embodiments may be used
with any type of glass sheet. In some aspects, embodiments are
useful for ion exchangeable, soda-lime silicate, EAGLE XG.RTM.,
0211-type, or alkali borosilicate glass sheet. In some embodiments,
the thickness of the glass sheet comprises about 100 .mu.m, 200
.mu.m, 300 .mu.m, 400 .mu.m, 500 .mu.m, 600 .mu.m, 700 .mu.m, 800
.mu.m, 900 .mu.m, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6
mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm,
2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3
mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8 mm, 3.9 mm, 4.0 mm, 4.1 mm,
4.2 mm, 4.3 mm, 4.4 mm, 4.5 mm, 4.6 mm, 4.7 mm, 4.8 mm, 4.9 mm, or
5.0 mm. In some embodiments, the bend in the glass sheet comprises
a radius of 100 .mu.m, 200 .mu.m, 300 .mu.m, 400 .mu.m, 500 .mu.m,
600 .mu.m, 700 .mu.m, 800 .mu.m, 900 .mu.m, 1 mm, 1.1 mm, 1.2 mm,
1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1
mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm,
3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8
mm, 3.9 mm, 4.0 mm, 4.1 mm, 4.2 mm, 4.3 mm, 4.4 mm, 4.5 mm, 4.6 mm,
4.7 mm, 4.8 mm, 4.9 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5
mm, 8.0 mm, 8.5 mm, 9.0 mm, 9.5 mm, 10.0 mm, 15 mm, 20 mm, 25 mm,
30 mm, 35 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 125
mm, 150 mm, or 200 mm. In some embodiments, the bend comprises a
curve that with a radius greater than 200 mm. In some embodiments,
the bend in the glass sheet comprises a radius from about 200 .mu.m
to about 5 mm, from about 200 .mu.m to about 3 mm, from about 200
.mu.m to about 2 mm, from about 200 .mu.m to about 1 mm, from about
300 .mu.m to about 5 mm, from about 300 .mu.m to about 3 mm, from
about 300 .mu.m to about 2 mm, from about 300 .mu.m to about 1 mm,
from about 400 .mu.m to about 5 mm, from about 400 .mu.m to about 3
mm, from about 400 .mu.m to about 2 mm, from about 400 .mu.m to
about 1 mm, from about 500 .mu.m to about 5 mm, from about 500
.mu.m to about 3 mm, from about 500 .mu.m to about 2 mm, or from
about 500 .mu.m to about 1 mm. In some embodiments, the bend
comprises a complex curve, such as a spline, or a combination of
curves of various radii.
[0048] In some embodiments, heating by the overall heating device
comprises resistance heating, combustion heating, induction
heating, or electromagnetic heating. In some embodiments, the
overall heating device comprises a kiln. In some embodiments, the
overall heating device comprises a furnace. In some embodiments,
the overall heating device comprises multiple heating devices,
which optionally, may be used in individually in different process
steps. In some embodiments, the overall heating device helps to
prevent stress in the glass sheet after the sheet is bent. In some
embodiments, the overall heating device is used to anneal the glass
sheet after it has been bent.
[0049] In some embodiments, overall heating comprises heating the
glass at a temperature below the glass transition temperature, the
annealing temperature, the deformation point, or the softening
point. In some embodiments, overall heating comprises heating the
glass at a temperature of about the glass transition temperature,
the annealing temperature, the deformation point, or the softening
point. In some embodiments, overall heating comprises heating the
glass at a temperature above the glass transition temperature, the
annealing temperature, the deformation point, or the softening
point. In some embodiments, overall heating of the glass sheet
comprises heating to a temperature wherein the viscosity of the
glass is from about 10.sup.10 to about 10.sup.21 Poise, about
10.sup.11 to about 10.sup.18 Poise, about 10.sup.13 to about
10.sup.15 Poise. In some embodiments, overall heating of the glass
sheet comprises heating to a temperature wherein the viscosity of
the glass is about 10.sup.7, 10.sup.8, 10.sup.9, 10.sup.10,
10.sup.11, 10.sup.12, 10.sup.13, 10.sup.14, 10.sup.15, 10.sup.16,
10.sup.17, 10.sup.18, 10.sup.19, 10.sup.20, or 10.sup.21. In some
embodiments, overall heating comprises heating the glass at a
temperature of about in a range from about 350.degree. C.,
400.degree. C., 450.degree. C., 500.degree. C., 550.degree. C.,
580.degree. C., 600.degree. C., 620.degree. C., 650.degree. C.,
700.degree. C., or 750.degree. C.
[0050] In some embodiments, overall heating of the glass sheet
comprises heating at a temperature about equivalent to the glass
transition temperature of the glass sheet. In some embodiments, the
glass transition temperature, T.sub.g, comprises the point at which
the viscosity of the glass is about 10.sup.13 Poise. In some
embodiments, the overall heating temperature comprises a range from
about -70.degree. C. to +70.degree. C. relative to the glass
transition temperature of the glass sheet. In some embodiments the
glass transition temperature is about 500.degree. C., 550.degree.
C., 580.degree. C., 600.degree. C., 620.degree. C., 650.degree. C.,
700.degree. C., or 750.degree. C.
[0051] Another aspect comprises the use of localized heating of the
glass sheet to provide control of the bending process. The
localized heating process comprises a key factor in optimizing the
curvature of the bend. The glass sheet has to be heated in a narrow
band to localize the deformation. The parameters that allow for
achieving a narrow band include the geometry and position of the
heating element (influencing the heat flux), the overall
temperature (if the overall temperature is low, glass outside the
bending region will not deform rapidly because of the heat transfer
by conduction coming from the heated region), and the heating
power, (high power values allow for rapid increases in temperature,
allowing for the maintenance of relatively low temperatures outside
the bend area). The ability to apply a higher local heating power
directly impacts the time required to bend the glass part. In the
case where the bending step is the bottle neck of the process
(other steps being progressive heat up and cooling) this may be an
advantage.
[0052] In some embodiments, localized heating comprises heating the
glass at a temperature below the annealing temperature, the
deformation point, the softening point, or the melting point. In
some embodiments, localized heating comprises heating the glass at
a temperature of about the glass transition temperature, the
annealing temperature, the deformation point, or the softening
point. In some embodiments, localized heating comprises heating the
glass at a temperature above the glass transition temperature, the
annealing temperature, the deformation point, or the softening
point. In some embodiments, overall heating of the glass sheet
comprises heating to a temperature wherein the viscosity of the
glass is from about 10.sup.7 to about 10.sup.14 Poise, about
10.sup.8 to about 10.sup.13 Poise, about 10.sup.9 to about
10.sup.12 Poise. In some embodiments, overall heating of the glass
sheet comprises heating to a temperature wherein the viscosity of
the glass is about 10.sup.7, 10.sup.8, 10.sup.9, 10.sup.10,
10.sup.11, 10.sup.12, 10.sup.13, or 10.sup.14. In some embodiments,
localized heating comprises heating the glass at a temperature of
about in a range from about 500.degree. C., 550.degree. C.,
580.degree. C., 600.degree. C., 620.degree. C., 650.degree. C.,
700.degree. C., 750.degree. C., 800.degree. C., 850.degree. C.,
900.degree. C., 950.degree. C., 1000.degree. C., 1050.degree. C.,
or 1100.degree. C.
[0053] In some embodiments, localized heating of the glass sheet
comprises heating at a temperature about equivalent to the
softening point of the glass sheet. In some embodiments, the
softening point comprises the Littleton softening point, comprising
the point at which the viscosity of the glass is about 10.sup.7.6
Poise. In some embodiments, the softening point comprises the
dilatometric softening point, comprising the point at which the
viscosity of the glass is about 10.sup.9 to about 10.sup.11 Poise.
In some embodiments, the softening point is determined by the Vicat
method (ASTM-D1525 or ISO 306), the Heat Deflection Test
(ASTM-D648), fiber elongation method (ASTM-C338), and/or a ring and
ball method (ASTM E28-67). In some embodiments, the localized
heating temperature comprises a range from about -70.degree. C. to
+70.degree. C. relative to the softening point of the glass sheet.
In some embodiments the softening point is about 620.degree. C.,
650.degree. C., 700.degree. C., 726.degree. C., 750.degree. C.,
800.degree. C., 850.degree. C., 900.degree. C., 950.degree. C., or
1000.degree. C.
[0054] Some embodiments allow the localized heating source to be in
contact or very close proximity to the glass sheet for precise
localized heating, minimizing overall glass temperature, and/or
preventing distortions in the glass sheet in order to provide good
control of the resulting shape and/or geometry. Localized heating
may comprise any number of mechanisms, for example via radiation,
conduction, or convection. Localized heating may be done via
infrared heater, flame torch or burner, resistance heating of an
element, or other means known to one of skill in the art. In some
embodiments, localized heating comprises use of radiative heating.
In some embodiments, localized heating comprises us of an IR
heater. IR heaters, as used in embodiments, may be used in
conjunction with any number of mirrors or other optics to produce a
narrow, focused beam on the glass.
[0055] In other embodiments, the localized heating device comprises
a conduction element, such as, but not limited to, a resistively
heated metal rod. In some embodiments, the conduction element
comprises a metal, metal oxide, carbon compound, intermetallic
compound, ceramic, or glass ceramic. In some embodiments, the
conduction element comprises platinum, nichrome, kanthal,
cupronickel, doped or undoped molybdenum disilicide, metal
ceramics, calrod, positive thermal coefficient ceramic, barium
titanate, lead titanate, molybdenum, or silicon carbide. As an
example, the embodiment in FIG. 2 comprises direct fired platinum
rods on ceramic support pedestals. The platinum rods conductively
heat the glass sheet, allowing a minimum area of the glass sheet to
be locally heated. While platinum conduction elements are shown in
the example, the only limitation on which materials could be
implemented as conduction elements is that the elements necessarily
need to be able to reach a temperature in the range of the
softening point of the glass being reshaped. A temperature near the
dilatometric softening point of the glass may be used to maintain
sheet flatness while still allowing reshaping. For example,
temperatures around the 3.5.times.10.sup.9 poise range are
necessary to reshape glass sheets of Corning Code 2318 alkali
aluminosilicate glass.
[0056] In some embodiments, the conduction element comprises a
shape that reflects the desired shape of the bend in the glass. In
some embodiments, multiple conduction elements are present to make
more complex shapes. In some embodiments, the conduction element
comprises a circular, oval, square, polyhedral, spline-like, or
ornamental cross-section. In some embodiments, the cross-section of
the conduction element comprises a circle. In some embodiments, the
radius of the circular cross section of the conduction element is
about 100 .mu.m, 200 .mu.m, 300 .mu.m, 400 .mu.m, 500 .mu.m, 600
.mu.m, 700 .mu.m, 800 .mu.m, 900 .mu.m, 1 mm, 2 mm, 3 mm, 4 mm, 5
mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm.
[0057] In some embodiments, the conduction element further
comprises a mechanical support. In some embodiments, the mechanical
support helps to maintain the structural integrity and straightness
of the conduction element while under load, and may further act as
a heat sink to allow for improved cooling of the conduction
element. In some embodiments, the mechanical support comprises a
metal oxide, carbon compound, intermetallic compound, ceramic, or
glass ceramic. In some embodiments, the mechanical support
comprises a ceramic or glass ceramic.
[0058] In some embodiments, the conduction element is optionally
coated with a release agent. The release agent may comprise any
compound or combination of compounds known to reduce or prevent the
glass sheet from adhering to the conduction element. In some
embodiments, the glass sheet is coated with compound to prevent
adhesion to the conduction element. In some embodiments, the
release agent comprises boron nitride, graphite or other carbon
forms, or mineral oil.
[0059] Another aspect comprises apparatus and methods comprising a
bending assistance device for decreasing bending cycle time,
decreased radius of curvature, and a lowering of the overall
temperature of the glass sheet during the bending process. In some
embodiments, the apparatus comprises a bending assistance device.
In some embodiments, the bending assistance device assists with the
glass bending process. In some embodiments, the bending assistance
device contacts the glass sheet on outside of the localized heating
area and on the opposite side of the localized heating area from
the support element. FIG. 3 shows a simplified schematic of an
embodiment wherein bending assistance devices are present at both
ends of a glass sheet. In this embodiment, the localized heating
element is a metal tube positioned below the glass sheet. Upon
activation of the localized heating element and when the glass
reaches bending temperature, the bending assistance devices can be
manually applied, automatically applied, or may assist gravity in
bending the glass sheet. FIG. 4 is a picture of an embodiment
comprising platinum tubes on ceramic supports along with an
embodiment of the bending assistance device, wherein the figure
shows the glass sheet after the bending process.
[0060] In some embodiments, the bending assistance device comprises
a metal, metal oxide, carbon compound, intermetallic compound,
ceramic, or glass ceramic. As noted above, the bending assistance
device may comprise any shape or structure that allows for it to
contact or apply force to the glass sheet and assist in bending the
glass and/or allows the device to perform the function of improving
the bend properties and/or bend characteristics, assists in bending
of the glass sheet at lower temperatures, and/or reduces the time
needed for bending the glass sheet. In some embodiments, the
bending assistance device comprises a roller, wheel, tube, rod, or
other element with a circular cross-section. In such embodiments,
the bending assistance device can change relative position on the
glass sheet without damaging the surface of the sheet as the sheet
bends. In some embodiments, the bending assistance device comprises
a plate or other element with a non-circular cross section that
maximizes contact with the glass sheet so as to minimize likelihood
of deforming the surface of the glass sheet.
[0061] Additionally, in some embodiments, the bending assistance
device may comprise one or more brackets that position the bending
assistance device and allow it to rotate and/or move as the glass
bends so as to maintain contact and/or pressure on the glass sheet.
The bending assistance device may comprise any material that
retains structural integrity at the temperatures in embodiments of
the claimed process. While shown in the embodiment in FIG. 3 making
a 90.degree. bend, the bending assistance device may be used to
make bends of any angle. The bending assistance device may assist
in preparing bend angles from greater than 0.degree. to about
170.degree., greater than 0.degree. to about 160.degree., greater
than 0.degree. to about 150.degree., greater than 0.degree. to
about 140.degree., greater than 0.degree. to about 130.degree.,
greater than 0.degree. to about 120.degree., greater than 0.degree.
to about 110.degree., greater than 0.degree. to about 100.degree.,
greater than 0.degree. to about 90.degree., greater than 0.degree.
to about 80.degree., greater than 0.degree. to about 70.degree.,
greater than 0.degree. to about 60.degree., greater than 0.degree.
to about 50.degree., greater than 0.degree. to about 40.degree.,
greater than 0.degree. to about 30.degree., greater than 0.degree.
to about 20.degree., or greater than 0.degree. to about
10.degree..
[0062] Another aspect comprises apparatus and methods comprising a
constraint device for preventing unwanted distortions to the glass
sheet and allowing for a lowering of the overall temperature of the
glass sheet needed during the bending process. In some embodiments,
the apparatus comprises a constraint device. In some embodiments,
the constraint device prevents the glass sheet bending or warping
outside of the bending region. In some embodiments, the constraint
device comprises an element that is moveable and only contacts the
glass sheet during the bending process. In some embodiments, the
constraint device comprises an element that is immoveable and only
contacts the glass sheet if it deforms during the bending process.
In some embodiments, both the bending assistance device and
constraint device are present.
[0063] FIG. 5A shows an unconstrained glass sheet subjected to
localized, radiative heating above the temperature necessary to
allow the glass to deform. As expected, the glass bends, but the
resulting bend causes deformation of the glass surface outside of
the bending area (FIG. 5B). In one embodiment, a method of avoiding
unwanted deformation outside of the bending area is to use a
constraint device is used to apply pressure to the glass sheet
outside the bending zone, in essence compressing the glass sheet
against the support element (FIG. 6A). FIG. 6B shows the resulting
structure of the glass sheet after bending when an embodiment of
the constraint device is used. As can be seen, the glass sheet near
the bend is much more uniform and has significantly less
distortion.
[0064] While not wanting to be constrained to any theory, it is
believe that the constraint element prevents movement of the glass
sheet outside the bending region and therefore, essentially "locks"
the sheet into its flat conformation, eliminating the possibility
of deformation during the localized heating cycle. More
specifically, in the theory of elastic plates, there is a
description of the compressed plate stability (see, e.g., Ronald D.
Ziemian, GUIDE TO STABILITY DESIGN CRITERIA FOR METAL STRUCTURES,
p. 1078, (Wiley, 2010), hereby incorporated by reference.)
.sigma. cr = .pi. 2 .psi. 3 ( 1 - v 2 ) E ( h b ) 2
##EQU00001##
where E is a Young module, .quadrature..nu. is a Poison's ratio,
.psi. is a parameter depended on boundary conditions of the plate,
wherein the minimal value of the parameter .psi.=0.1, h is the
thickness of the plate and b the width of the area in compression
("5" in FIGS. 5 and 6). This case corresponds to conditions where
there is no cold length, (denoted as "7" in FIGS. 5 and 6),
meaning, the zone of localized heating goes to the edge (reference
no. "7"=0).
[0065] The value of .sigma..sub.cr determines a limit above which
the plate is not stable and subject to a deformation. The analogy
is not strictly valid for glass bending because, as the material is
not purely elastic, it indeed dissipates part of the stress by
viscous relaxation. However, in glass submitted to a non-uniform
temperature field, compressed stresses can be estimated by the
following formula:
.sigma..sub.y=E.alpha..DELTA.T [0066] where .alpha. is the glass
coefficient of thermal expansion ("CTE"), .DELTA.T is a temperature
difference between the heated zone and the rest part of the glass
sheet. One can then see that the parameters impacting the stability
of the glass sheet upon localized heating are 1) glass
thickness--the thinner the glass, the lower the stress above which
out of plane deformation occurs; 2) glass CTE--instabilities are
favored for high CTE compositions, such as ion exchangeable
glasses; and 3) local temperature gradient--increasing the
temperature difference between the preheating environment and the
heated area allows for a tighter radius of curvature and reduced
cycle time, but also favors instability.
[0067] The use of a constraint device impacts the stability of the
glass sheet in a number of ways. As illustrated in FIG. 7,
decreasing the preheating temperature tends to lead increase the
likelihood of instability. However, as noted previously, for
surface quality reasons it is desirable to minimize this
temperature, an observation being that below the glass transition
temperature is a good practice. For example, it has been shown that
in embodiments comprising a constraint device, it is possible to
decrease the preheating temperature down to 520.degree. C., using a
glass having a glass transition temperature of 580.degree. C.
[0068] The application of the constraint device is generally done
only during the localized heating step. In some embodiments, the
constraint device is applied onto a portion or the whole width of
the bend, and located as close as possible to the locally heated
area without marring the surface of the glass. In some embodiments,
the distance between the load and the locally heated area has to be
within a range bounded by the lower limit distance, which is
defined by the distance wherein marks appear due to the contact of
heated glass by a solid material. Practically, the limit comprises
a distance of about 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm,
9 mm, 10 mm, 15 mm, or 20 mm. In some embodiments, the distance
between the load and the locally heated area has to be within a
range bounded by the upper limit distance, which is defined by the
distance wherein unacceptable deformation occurs between the bend
and the constraint device. Practically, for preheating temperatures
10.degree. C. below the transition, and local heating rate above
150.degree. C./min, the limit comprises a distance of about 10 mm,
15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60
mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, or 100 mm.
[0069] The contact pressure between the load and the glass
comprises a force moderate enough to avoid the creation of optical
defects. The constraint device may be applied to the top, bottom or
both faces of the glass and may comprise any material that retains
structural integrity at the temperatures in embodiments of the
claimed process (FIGS. 8A-D). Examples of materials used in the
embodiments of constraint devices, but are not limited to, ceramic,
glass ceramic, inorganic compounds, carbon-based compounds, and
glasses, and combinations thereof. The contact pressure required to
maintain a flat glass surface is on the order of about 100, 150,
200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800
N/m.sup.2, and may be brought about by any of the means
constituting the different embodiments. Additionally, the contact
material may comprise, but is not limited to, glass ceramic,
stainless steel, or porous or fiber board ceramic.
[0070] The constraint device may also comprise a heat sink, which
may allow for increased temperature variations between the
localized temperature and overall temperature of the glass sheet,
or thermal isolation of the bend and flat regions of the glass
sheet. In embodiments where the constraint device also comprises a
heat sink, the constraint device may comprise a metal piece to act
in both a constraint and thermal sink capacity.
[0071] In another embodiment, the constraint device comprises a
rigid body positioned above the glass and above the support element
and prevents the glass sheet from freely deforming during the
bending process (FIGS. 9A and 9B). In this embodiment, a minor gap
may be present between the glass sheet and the constraint device,
and contact between the constraint device and the glass sheet only
takes place when deformation of the sheet exceeds the gap spacing.
An advantage of this embodiment is that contact with the glass is
only partial and only in areas where the glass deforms. In some
embodiments, the spacing between the glass and the rigid constraint
device comprises about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100,
150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750,
800, 850, 900, 950, or 1000 .mu.m.
EXAMPLES
Example 1
[0072] A Wilt furnace having a 600.times.1700 mm base area was used
to perform experiments. The furnace could be raised and lowered
over the base for accessibility to the bending system. Two platinum
rods or tubes were positioned parallel to each other on the furnace
floor and at a separation distance determined by the final shaped
length of the glass sheet.
[0073] The platinum tubes were supported off the furnace floor on
each end by refractory V-blocks. A refractory plate or frame
mounted on refractory blocks was placed between the tube support
blocks to support the glass sheet. A ceramic tube or rod was
inserted into the platinum tube as a mechanical support to maintain
the straightness of the platinum tubes and keep them from bending.
Current was supplied to the platinum tubes by using platinum straps
welded to the tube ends with the other ends connected to cooled
copper electrical buss blocks. A transformer stepped down the line
voltage and increased the amperage going into the platinum tubes. A
controller was connected to a semiconductor-controlled rectifier
("SCR") to control the power and the resulting temperature
generated by the platinum tubes. Thermocouples were placed in
contact at the center area of each tube and at each tube end. The
controller was controlled by one of the center thermocouples acting
as a "control thermocouple." A seventh thermocouple was placed
under the glass sheet to read the furnace internal temperature. The
furnace itself had two internal thermocouples with one supplying
feedback to the controller for the furnace.
[0074] An optional release agent was applied to the tubes to help
keep the glass from sticking to the platinum tubes at elevated
temperatures. The release agent used was a boron nitride spray
(EKamold.RTM.EP EKS Ceramics GmBH). The boron nitride was lightly
applied to the platinum tubes, and then the platinum tubes were
heated to 200.degree. C. for 10 minutes to bake on the release
agent. Initially, some release agent residue would appear on the
glass sheet after bending, but if the control temperature was
maintained below 700.degree. C., then no residue was observed.
Alternatively, several glass sheets were prepared for acid etching
studies, and after the etching process the residue was removed.
[0075] The glass sheet was scribed and cut to the particular size
of interest. Prior to the glass sheet placement on the refractory
plate or frame, the refractory setter plate was leveled and
accurately positioned between the platinum tubes. The setter plate
used was a 1/4'' thick refractory silica board (RSLE-57
manufactured by ZIRCAR), which had been cut to size. Once the glass
sheet had been placed on the setter plate, the thermocouples are
positioned to be in contact with the platinum tubes on each end and
one in the center. Alignment of the platinum tubes was checked
along with the sheet position so that the correct shape could be
formed.
[0076] The furnace is closed and taken to a preheat temperature of
525.degree. C. and allowed to reach thermal equilibrium. Power is
applied to the tubes and a temperature is selected that allows the
glass to soften enough to bend but not hot enough to distort other
areas of the sheet. Initial trials involved bending the glass sheet
via its own weight. Once the sheet has under gone bending or
reshaping the power is removed from the platinum tubes and the
glass sheet is allowed to cool in the furnace.
Example 2
[0077] While initial trials involved bending the glass sheet via
its own weight and gravity, a mechanical gravity assisted shaping
tool was also implemented. A mechanical bending device was designed
to assist with the glass bending process. This device comprised a
ceramic tube and two support end brackets that allowed the ceramic
tube to "roll" via gravity over the sheet edge as it softened. This
bend assisting device enabled sheet edges to be shaped at lower
temperatures and at faster time intervals.
[0078] Using this device also allowed shorter edge lengths of the
glass sheet to be bent as compared to earlier trials without the
device. Previously, with shorter sheet edges, gravity bending alone
necessitated either longer time intervals or higher temperatures.
For example, if a sheet edge shorter than approximately 100 mm was
required on the final piece, it was most practical to scribe the
edge and laser cut to size after bending. However, the laser
cutting would have added an additional step to the process, and
some cuts were poor due to residual stress in the sheet especially
around the bend area. Using the 100 mm long sheet edge, which
provided enough glass weight to produce a good geometrical bend
radius, took on the order of 15 minutes to achieve the bend at
temperatures .apprxeq.730.degree. C. With the addition of the bend
assisting device, it was possible to successfully bend sheet-edge
lengths of 10 mm in around 3 to 4 minutes at 700.degree. C. for 5,
3 and 2 mm bend radii (see FIGS. 10, 11, 12, and 13).
[0079] Comparatively, attempting to bend a sheet edge length of 10
mm without the bending device increased the time interval to 30
minutes and a platinum tube temperature above 800.degree. C. The
resulting bend was non-uniform along the width of the sheet, with
some distortion along the sheet center surface and higher
contamination on the bend surface from the release agent.
Therefore, the bend assisting device enabled good geometrical bends
at lower temperatures and faster times.
[0080] After the glass sheet was positioned on the setter plate,
the thermocouples were placed along the platinum tubes and the
alignment of the platinum tubes was checked, the bend assisting
device was placed on the sheet. The bend assisting device was
positioned on the top glass sheet surface near the outer edge of
the sheet. The ceramic tube support brackets were designed to
attach to the platinum tubes at each end beyond the sheet width.
These brackets enabled the ceramic tube to sit on the glass surface
near the outer most edge of the glass sheet and move freely. When
the glass sheet was locally heated and started to soften, the
ceramic tubes were able to move downward via gravity as the sheet
bends. The added weight of the ceramic tubes assisted in bending
the sheet, which takes less time and temperature, and helped to
apply even stress to the glass, allowing for a more controlled
bend.
[0081] When the glass sheet and bending device were in position,
the Wilt furnace was ramped up to 580.degree. C. and held at this
temperature throughout the bending cycle. The thermocouple
temperatures were plotted using data acquisition software that
allowed for monitoring of the thermal profile of the platinum tubes
and also recorded the Wilt furnace temperature. As the Wilt furnace
temperature reached equilibrium at 580.degree. C., the platinum
tube power control was energized. The controller for the direct
fired platinum tubes was ramped up to 680.degree. C. at a rate of
50.degree. C. per minute. The PID control parameters were tuned for
the specific size of platinum tubing in order to minimize any
temperature overshoot and maintain tight control of the
temperature. Once the 680.degree. C. temperature was achieved, it
took approximately four minutes for the sheet to fully bend to the
desired shape. The temperature along the length of each tube was
somewhat variable, but all thermocouples read within the 680 to
700.degree. C. range.
[0082] The sheet started to bend almost immediately once the
platinum tubes reached the 680.degree. C. temperature. The
additional several minutes was required to ensure that the bend was
complete on both sides to the desired finial angle. Bend angles up
to 90 degrees were achieved with angles less than 90 degrees made
by using a refractory plate to stop the glass edge from bending any
further. More complex shapes and larger angles are possible by
using different platinum tube sizes and shapes along with
refractory forms that allow specific bend angles. The direct-heated
platinum tubes enabled reshaping the glass sheet at a lower
temperature, avoiding embossing or the creation of surface defects
from contact, which is not the case with using molds for reshaping
glass at higher temperatures.
[0083] After the sheet was fully bent to the desired angle, power
was shut off to the platinum tube and the sheet was allowed to cool
to the internal furnace temperature of 580.degree. C. The sheet and
furnace were allowed to slowly cool to below 250.degree. C. before
opening the furnace and allowing a faster cooling rate. This slow
cooling took several hours to achieve, but it had been observed
that taking a bent sheet out while the furnace is above 300.degree.
C. could cause the sheet to crack.
[0084] In some cases, the bending area could contain residual
stress even when the glass was allowed to cool slowly. Therefore,
an optional step of annealing the sheet after bending, either with
the sheet in place or by annealing after it was removed, was done.
It was found that annealing was best done after the sheet had been
removed from the bending system and was laid on a flat surface with
the bend edges upward. This prevented bowing of the sheet during
the anneal cycle with the ceramic bend assisting device still on it
and optionally applying tension to the sheet.
Example 3
[0085] On a commercial scale, a manufacturing process requires a
much faster cycle time to make the bends, and then post-heat treat.
One possible process is to use a Lehr or tunnel kiln to preheat the
glass sheet, move the sheet to a forming platform, bend the sheet,
and then place the sheet back in the same kiln for post-thermal
treatment. This setup avoids making the bending apparatus the
bottle-neck of the commercial process.
[0086] Another possibility is to have the sheet come through a Lehr
or tunnel kiln, bring the platinum tubes up to the sheet while at
the same time bringing the bending assisting device into contact
with the glass, and bending the sheet without moving it from the
conveyor belt. While more complicated, this process allows for
rapid reshaping of the glass sheets in an assembly line
fashion.
[0087] An alternative approach is to use a furnace to preheat the
glass sheet, a second furnace for bending, then after bending,
transfer the glass to an annealing furnace. If the glass sheet is
on a refractory plate which does not lose temperature between
transfers, for example a silica plate, then the glass sheet can be
transferred without cracking. A benefit of the direct-fired
platinum tubes is that the lower surrounding temperatures enable
shuffling glass sheets to and from the bending apparatus with less
loss of heat and less potential for cracking. With the short
bending times, embodiments of the claimed process allow
manufacturing of multiple parts and a higher throughput.
* * * * *